1. No category

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Introduction to Digital
Communication
Ingo Foldvari
Academic Program Manager
National Instruments California
Phone: 760 691 0877
Email: [email protected]
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Wireless Communication Devices
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NI USRP and LabVIEW
A Platform for Software Defined Radio Prototyping and Exploration
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NI RF and Communicatons Fundamentals
1.
Introduction to RF & Wireless Communications Systems
2.
RF and Microwave Spectral Analysis
3.
Analog Modulation
4.
Digital Modulation
5.
Communications Systems
6.
Modulation Measurements
7.
Communication Standards
8.
Understanding RF & Microwave Specifications
9.
RF & Communications Terminology and Glossary
10.
RF & Communications Resources
11.
See Also - RF Fundamentals 3-Day Training Course
12.
Ressource: http://www.ni.com/white-paper/3992/en
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RF Handbook
Ideal for learning or refreshing your knowledge of RF & Comm.
•
Practical information, theoretical foundation
Demonstrations and lab exercises based on
•
NI LabVIEW
•
LabVIEW Modulation Toolkit
•
NI IF & RF Communications Hardware Platform
Full Color Version
•
Orderable Book:
http://www.lulu.com/content/1133250
•
Free PDF Download:
http://www.lulu.com/product/file-download/rf-communications-handbook/1714782
Black&White (low cost) Version
•
Orderable Book:
http://www.lulu.com/content/1193352
•
Free PDF Download:
http://www.lulu.com/product/file-download/rf-communications-handbook-(bw)/1714760
LabVIEW VIs (free download):
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http://www.lulu.com/content/1302357
6
Online Community
https://decibel.ni.com/content/groups/ni-usrp-example-labview-vis
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Wireless Digital Communication
modulated
IQ waveform
IQ waveform
analog
digital
analog
00100100
00100100
User
User
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digital
Basics of Frequency Spectrum
100
MHz
1GHz
Wavelength Calculation
Speed _ of _ Light (meters / sec)
 Wavelength (meters )
Frequency ( Hz)
FM Radio Example
299 792 458 m/s 300 M m/s

 3 m wavelengt h
100MHz
100MHz
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¼ wave antenna = .75 m =
2.5 feet
NI USRP and LabVIEW
A Platform for Software Defined Radio
Prototyping and Exploration
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A Highly Productive Graphical Development Environment for Engineers and Scientists
Hardware APIs
Analysis Libraries
Custom User Interfaces
Deployment Targets
Technology
Abstractions
Models of Computation
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Models of Computation
C / HDL Code
Dataflow
Simulation
Statechart
LabVIEW
LabVIEW
LabVIEW
LabVIEW
Desktop
``
Real-Time
FPGA
MPU/MCU
Personal Computers
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Textual Math
PXI Systems
CompactRIO
12
Single-Board RIO
Custom Design
Review: Creating a Virtual Instrument
•
•
LabVIEW programs are called
Virtual Instruments or VIs.
Each VI has two windows
•
Front Panel  User Interface
(UI)
o
o
•
Controls = User Inputs
Indicators = Outputs
Block Diagram  Program
Code
o
o
Data travels on wires from
controls through functions to
indicators
Blocks execute by Dataflow
Front
Panel
Block Diagram
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Review: Front Panel Controls Palette
(Controls & Indicators)
Control:
Numeric
Front
Panel
Indicator:
Gauge
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Review: Block Diagram Functions Palettes
Structure:
While Loop
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Review: Block Diagram – Wires
•
•
•
Transfer data between block diagram objects through wires
Wires are different colors, styles, and thicknesses, depending on
their data types
A broken wire appears as a dashed
black line with a red X in the middle
DBL Numeric
Integer Numeric
String
Boolean
Scalar
1D Array
2D Array
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Review: Block Diagram Terminals
Front Panel Window
Numeric
Controls
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Block Diagram Window
Numeric
Indicator
17
Review: Tools Palette
• Recommended: Automatic Selection Tool
• Tools to operate and modify both front panel and block diagram
objects
Automatic Selection Tool
Automatically chooses among the following tools:
Operating Tool
Positioning/Resizing Tool
Labeling Tool
Wiring Tool
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Review: Status Toolbar
Run Button
Continuous Run Button
Abort Execution
Additional Buttons on
the Diagram Toolbar
Execution Highlighting Button
Retain Wire Values Button
Step Function Buttons
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Review: Dataflow Programming
• Block diagram execution
– Dependent on the flow of data
– Block diagram does NOT
execute left to right
• Node executes when data
is available to ALL input
terminals
• Nodes supply data to all
output terminals when
done
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Review: Context Help Window
•
•
Help»Show Context Help, press the <Ctrl+H> keys
Hover cursor over object to update window
Additional Help
– Right-Click on the VI icon
and choose Help, or
– Choose “Detailed Help.” on
the context help window
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Review: Textual Math with the MathScript Node
•
•
•
•
Implement equations and algorithms textually
Input and Output variables created at the border
Generally compatible with popular m-file script language
Terminate statements with a semicolon to disable immediate output
(Functions»Programming»
Structures»MathScript)
Prototype your equations in the interactive MathScript Window.
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Review: The Interactive MathScript Window
•
Rapidly develop and test algorithms
• Share Scripts and
Variables with the Node
• View /Modify Variable
content in 1D, 2D, and 3D
Output
Window
Variable
Workspace
View/Modify
Variable Contents
m-file Script
User Commands
(LabVIEW»Tools»MathScript Window)
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Programming Demo
DATA VS. WAVEFORMS
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NI USRP Under the Hood
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System Setup
NI USRP-2920
NI USRP-2920
Transmitter
Receiver
•
•
•
•
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USRP control (Tx & Rx)
Modulate Tx signal
Demodulate Rx signal
Reconstruct message
NI USRP-2920 Hardware Diagram
Analog RF Transceiver
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Fixed Function FPGA
27
PC
NI USRP
Tunable RF Transceiver
Front Ends
 Frequency Range
50 MHz – 2.2 GHz (NI-2920)
2.4 GHz & 5.5 GHz (NI-2921)
Applications





FM Radio
TV
GPS
GSM
ZigBee
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



Signal Processing
and Synthesis
 NI LabVIEW to
develop and explore
algorithms
 NI Modulation Toolkit
and LabVIEW addons to simulate or
process live signals
1 Gigabit Ethernet
Connectivity
Safety Radio
OFDM
Passive Radar
Dynamic Spectrum Access
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 Plug-and-play
capability
 Up to 25 MS/s
baseband IQ
streaming
Graphical Implementations and MathScript RT
NI USRP-2920
NI USRP-2920
Transmitter
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Receiver
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NI-USRP Driver Software
Initialize
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Configure
Write IQ
30
Close
Communications Design Topics
•
Education
•
•
•
•
Research
•
•
•
•
Introductory Communications
Digital Communications
Antenna Theory
Physical layer research (SISO & MIMO)
Cognitive Radio & Dynamic Spectrum Access
RF transmit or receive applications
Defense
•
•
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Spectral Monitoring
Prototyping Communications Systems
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Complete
RF Prototyping
Solution
Programming Demo
TRANSMIT WAVEFORM
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Programming Demo
TRANSMIT WAVEFORM WITH
COERCED HW SETTINGS
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Why IQ?
•
It is difficult to vary precisely the phase of a highfrequency carrier sine wave in a hardware circuit
according to an input message signal.
•
A hardware signal modulator that manipulates the
amplitude and phase of a carrier sine wave would
therefore be expensive and difficult to design and build
•
HW circuit that uses I and Q waveforms are more flexible
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Quadrature Modulation
Ac cos(2f ct   )
Amplitude
Frequency
Phase
Angle
(Frequency = Rate of change of Angle)
I (t ) cos(2f ct )  Q(t ) sin(2f ct )
Note:
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I and Q capture magnitude and phase information
I refers to in-phase data (because the carrier is in phase)
Q refers to quadrature data (because the carrier is offset by 90 degrees).
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IQ Modulator
IQ is the Cartesian representation of
a vector from a Polar Coordinate System.
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Programming Demo
PHASOR PLOT
TRANSMIT COMPLEX IQ WAVEFORM
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Modulation Basics
•
RF communication systems use advanced forms of
modulation to increase the amount of data that can be
transmitted in a given amount of frequency spectrum.
•
Signal modulation can be divided into two broad
categories:
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•
analog modulation (analog audio data is modulated onto a carrier
sine wave )
•
digital modulation (digital bits modulated onto a carrier sine
wave)
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Modulation Basics
•
Carrier sine wave needs to change in amplitude,
frequency, and phase in order to encode information
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Modulation Example – AM Radio
Audio Signal
20Hz – 20kHz
Baseband IQ
AM Radio Signal
Audio
Radio
IQ Mixing
Message (Baseband)
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LabVIEW Software
Frequency
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NI USRP Hardware
Carrier
More than just the message: Packet Structure
GUARD
SYNC
PCKT
BAND
SEQ
NUM
DATA
PAD
Field
Length
[bits]
Description
Guard Band
30
Allow initialization of Rx PLL, filters,
etc
Sync Sequence
20
Frame and Symbol Synchronization
Packet Number
8
Range: 0-255 Used for reordering of
packets and detection of missing
packets
Data
64 - 256
Variable length data field. Length
detected dynamically at Rx end
Pad
20
Allows for filter edge effects.
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Modulation Basics - Digital Modulation
the “how one sends” of “what” one sends
IQ Baseband Data
Bit Stream (32 Bits)
Symbol Stream (4-QAM)
(2 bits/symbol16 IQ symbols)
To RF
Amplifier
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Mapping Bits to Symbols
In digital modulation, the number of bits sent per second is called Bit
Rate - the higher the bit rate, the faster the communication speed.
One way for digital communication systems to support a higher bit rate
is to encode multiple bits of information in the variations of the carrier
signal.
Symbol maps for 4-ASK modulation (left) and 4-PSK modulation (right)
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4-QAM Symbol Map
•
Four-QAM uses four combinations of
phase and amplitude.
•
Each combination is assigned a 2-bit
digital pattern.
Example
•
generate the bit stream (1,0,0,1,1,1)
•
each symbol has a unique 2-bit pattern
•
bits are grouped in two’s so that they
can be mapped to the corresponding
symbols
•
(1,0,0,1,1,1) is grouped into the three
symbols (10,01,11).
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10
11
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00
01
Pulse-Shaping Filter
In communications systems, two important requirements of a wireless
communications channel demand the use of a pulse shaping filter.
•
Generating bandlimited channels (reduce bandwidth)
•
reducing inter symbol interference (ISI) from multi-path signal reflections
Both requirements can be accomplished by a pulse shaping filter which is
applied to each symbol
A sync pulse meets both of these requirements because it efficiently utilizes
the frequency domain to utilize a smaller portion of the frequency domain,
and because of the windowing affect that it has on each symbol period of a
modulated signal.
Time vs. Frequency Domain for a Sinc Pulse
Pulse-Shape Filtering in Communications Systems
http://www.ni.com/white-paper/3876/en
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Pulse-Shaping Filter
Sharp transitions from one symbol to the next occur when filtering is not applied.
Sharp transitions in any signal result in high-frequency components in the frequency
domain resulting in significant channel power outside of the defined bandwidth.
Applying a pulse-shaping filter to the modulated sinusoid, the sharp transitions are
smoothed and the resulting signal is limited to a specific frequency band
Phase and Amplitude Transitions in an Unfiltered Modulated Signal
Smoothed Phase and Amplitude Transitions in a Filtered Modulated Signal
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Frequency Domain of Unfiltered Signal
Frequency Domain of Filtered Signal
Programming Demo
AM MODULATION
4-QAM SYMBOL MAPPING
PSK PULSE-SHAPING FILTER
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NI-USRP Driver Software
Initialize
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Configure
Start
Read IQ
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Stop
Close
NI-USRP Driver Software
Initialize
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Configure
Start
Read IQ
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Stop
Close
Programming Demo
RECEIVE COMPLEX IQ
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Digital Communication System
NI Modulation Toolkit
NI USRP
NI Modulation Toolkit
NI USRP
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Communications Design in LabVIEW
LabVIEW Modulation Toolkit
•
Analog and Digital modulation formats
•
•
•
•
Visualization
•
•
BER, MER, EVM, burst timing,
frequency deviation, ρ (rho)
Impairments
•
•
•
2D and 3D Eye, Trellis, Constellation
Modulation Analysis
•
•
AM, FM, PM
ASK, FSK, MSK, GMSK, PAM, PSK, QAM
Custom
Additive White Gaussian Noise (AWGN)
DC offset, Quadrature skew, IQ gain
imbalance, phase noise
Equalization, Channel Coding, Channel
Models
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Programming Demo
PSK PHASE SHIFT
RECEIVE AND DECODE COMPLEX IQ
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ADDITIONAL DEMOS
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DEMO
FM RADIO
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Decode & Hear Live FM Radio
Mono
Audio
Left + Right
19kHz
Stereo
Pilot
(10%)
Stereo Audio
Left - Right
Direct Band
RBDS (10%)
(5%)
0
30
Hz
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15
kHz
23
kHz
38
kHz
57
kHz
53 58.35 67.65
kHz kHz kHz
Audos Subcarrier
(10%)
76.65
kHz
92
kHz
99
kHz
DEMO
PACKET BASED TRANSCEIVER
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Packet Based Transceiver
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NI PXI RF & NI USRP
Case Studies and User Solutions
ni.com
NI PXI RF
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NI RF and Communications Market
RF Test & Measurement
• Calibration
• Low Phase Noise
• Precise measurement
• Real-time
• High Bandwidth
Communications Design
• Low Cost
• Flexible
• Portable
• Radio
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•
•
•
The networking and connectivity subsidiary of Qualcomm, Inc.
Leading provider of wired and wireless technologies
Serving mobile, computing, consumer electronics and networking
channels
GPIO
2.4/5 GHz
11ac
Radio
Front
End
WLAN
RF
CPU and
Memory
SOC, MAC
and PHY
PCIE
Power
Management
Synthesizer
802.11ac Device Block Diagram
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GPIO
PCIE
3.3 V
REF CLK/
Crystal
RF Standards—Increasing Complexity
802.11a + b + g
+ 802.11n
100+ Combinations
1,000+ Combinations
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+ 802.11ac
10,000+ Combinations
Software –Designed Approach
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NI PXIe-5644R Hardware Front Panel
RF Input
65 MHz – 6 GHz
80 MHz BW
RF Output
65 MHz – 6 GHz
80 MHz BW
Reference In/Out
Calibration In/Out
Always keep the calibration
cable connected
Trigger
LOs In/Out
Independent
In & Out
MIMO Support
Digital I/O
24 channels
Up to 250 Mbps
Additional triggering
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Vector Signal Transceiver/Device Under Test
Integration
Qualcomm Atheros
802.11ac Device Under Test
Tx
Rx
RF-out
RF-in
RF-in
RF-out
Digital
I/O
VSG
Digital
I/O
Digital Device
Control
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VSA
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EVM* (dB) vs. Average Output Power
-45
-25
-5
-45
15
-18
-18
-23
-23
-28
-28
-33
-33
-38
-38
-43
-43
-48
-48
-5
15
NI PXI Vector Signal Transceiver
Traditional Instrumentation
* Error Vector Measurement: http://www.ni.com/white-paper/3652/en
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-25
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Qualcomm Results
802.11a + b + g
+ 802.11n
+ 802.11ac
Early 2000s
Traditional Rack and Stack
2007
NI PXI RF Instrumentation
2012
NI PXI VST
10X
200X Faster Than Traditional
20X
“At Qualcomm Atheros, instrumentation flexibility and to-the-pin control are critical for
keeping our RF test process as efficient as possible, and we're pleased with the
performance gains we've seen when testing with NI's new vector signal transceiver.”
Doug Johnson, Director of Engineering at Qualcomm Atheros
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Lab Ready
Digital Communications Labs
Communications Systems Labs
by Dr. Robert Heath, UT Austin
1
2.1
2.2
3
4
5
6
7
8
by Dr. Sachin Katti, Stanford
AWGN Simulator
Modulation /Demodulation
Pulse Shaping
Energy Detection
Equalization
Frame Detection
Intro to OFDM
Frequency Correction &
Sync
OFDM Channel Coding
1 Source Coding
2 Packet Communication, Sync,
and Channel Correction
3 Modulation
4 Demodulation
5 Design Challenge:
Packet based Transceiver
(Ships in Bundle)
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(FREE: ni.com/courseware)
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NI USRP at Stanford University
Student Course Feedback:
“
Awesome class! I really enjoyed the lectures,
where I learned a lot, and the labs were really
cool because we got to use the hardware.
… I am glad that I took this class!
“
Source: Stanford EE 49: Teaching Evaluations (Spring Quarter 2011)
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Stanford University - Networked Systems Group
Needs:
• Exposure to real-world signals
• Recruit students to
RF/Communications early
• Prepare students for research
Solution:
• SDR Platform
• Lower learning curve
• Maintainable
• Affordable
“The course evaluations for our class was fantastic.
Students rated the class 4.94/5.0, likely one of the
highest ratings among all classes in the School of
Engineering at Stanford.”
Dr. Sachin Katti, ECE
Stanford, CA
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NI USRP Research Case Study:
Cognitive Radio & Whitespace
LabVIEW Graphical System Design
•
•
•
Spectral sensing with blind detection
GPS geographic localization
Adaptive spectrum utilization
“LabVIEW software and the NI USRP hardware are key
components of this research project, allowing the team
to rapidly prototype and successfully deploy the first
cognitive radio test bed of this kind.” Dr. Paulo
Marques, COGEU
Aveiro, Portugal
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MIMO Radio Prototyping
Plug and play 2x2 MIMO
• Driver based
synchronization
• Reference designs available
•
•
•
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Maximal Ratio Combining
Alamouti Coding
73
2x2 MIMO - Alamouti Coding
6x6 MIMO Testbed
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NI USRP Research Case Study:
Dr. Robert Heath
NI USRP 8x8 MIMO Testbed
•
•
•
•
Director WNCG
University of Texas at Austin
External
Clock
Adaptable from 2x2 to 8x8
Algorithm design in MathScript RT
128 subcarrier OFDM, 4 QAM, spatial Network
Cable
diversity
Independently clocked, phase
Host
Computer
coherent Tx & Rx
Network
Cable
External
Clock
75
Transmit
PPS in
USRP
TX 1
MIMO Cable
USRP
TX 2
USRP
TX 3
MIMO Cable
USRP
TX 4
USRP
TX 5
MIMO Cable
USRP
TX 6
USRP
TX 7
MIMO Cable
USRP
TX 8
Gigabit
Ethernet
Switch
Network
Cable
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Ref in
Receive
USRP
Rx 1
MIMO Cable
USRP
Rx 2
USRP
Rx 3
MIMO Cable
USRP
Rx 4
USRP
Rx 5
MIMO Cable
USRP
Rx 6
USRP
Rx 7
MIMO Cable
USRP
Rx 8
NI USRP Research Case Study:
Physical Layer Prototyping
•
•
•
Dr. Murat Torlak
Continuously monitoring Demodulate
multiple wifi channels
Demodulation and
descrambling of 802.11b
beacon signals
Identification of hotspots,
tracking relative power
levels
Descramble
802.11b SSID Decoding
Carrier
Detection
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Frequency
Offset
Estimation &
Correction
Demodulation
&
Descrambling
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Interpret the
frame for
SSID
NI USRP Research Case Study:
Algorithm Research
Cleaning Up “Dirty RF”
Established a live, over-the-air
communication OFDM link
•
•
•
1024 subcarriers
256-QAM modulation per subcarrier
bit rate of about 1.4 Mbps on laptop
LabVIEW host-based VIs
•
•
•
Imported m-file scripts
Extensive use of Mathscript RT
~2 month timeframe
•
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reducing project time by 2/3
77
NI USRP Research Case Study:
TU-Dresden: “Dirty RF”
Established a live, over-the-air
communication OFDM link
•
•
•
1024 subcarriers
256-QAM modulation per subcarrier
bit rate of about 1.4 Mbps on laptop
LabVIEW host-based VIs
•
•
•
Imported m-file scripts
Extensive use of Mathscript RT
~2 month timeframe
•
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reducing project time by 2/3
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Prof. Athanassios Manikas
NI USRP Research Case Study:
Comm & Array Processing Chair
Imperial College, London
Position Detection & Localization
•
•
•
•
Testing MUSIC direction finding
algorithm
Rapid prototyping in LabVIEW with
MathScript RT
Synchronized up to12 USRP devices
Reference provides continuous phase
alignment compensation
Direction Finding (uniform linear
array)
USRP
RX 1
External
Clock
Ref in
USRP
RX 2
Network
Cable
Host
Compute
r
Network
Cable
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PPS
in
Gigabit
Ethernet
Switch
USRP
RX 3
USRP
RX 4
USRP
TX
Calibration
Signal
Research: Downloadable Reference Designs
8x8 MIMO-OFDM
ni.com/usrp
GPS
Simulation
Tx
RF Direction Finding
& Localization
RF Record &
Playback
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